Effects of die pad anchoring on package interfacial integrity

The effects of anchoring the die pad to the epoxy molding compound to improve the package interfacial integrity are addressed. The designs considered varied from simple circular holes dispersed at the four corners of the die pad to longer slots distributed along the periphery of the die. 3-D finite element models were constructed to simulate the residual stress profiles within the various molded configurations. Interfacial delamination was artificially induced at selected locations of the die pad by nodal decoupling. The simulation results were compared with acoustic tomograph scans of the packages to assess any correlation between the predicted high stress profiles and the extent of delamination observed. The introduction of an anchor in the die pad provided various degrees of stress relief to the silicon die, depending on the anchor geometry. Although the effects were localized, the ensuing stress reduction was sufficient in some cases to avoid the initiation of delamination. Finite-element results also pinpointed other areas of high stress concentration, which acted as potential sites where delamination could initiate and propagate. Based on these results, design criteria were formulated to dictate the most efficient pattern of holes and slots that would provide the best anchoring properties to the molding compound